The aim of the present invention is to propose a process for the production of milk from fruit kernels which can be used in the food sector, especially milk from fruit kernels of high thermal stability and having good self-emulsifying properties which allow the reconstitution of fine and stable emulsions.
To this end, in the process for the production of milk from fruit kernels according to the present invention:
fruit kernels are ground in water in order to obtain an aqueous dispersion of ground kernel matter,
an aqueous extraction is performed on the ground kernel matter dispersion,
the insoluble matter of the aqueous extract is separated,
a protein and/or lipid rich fraction is isolated from the aqueous extract containing medium,
the said fraction is homogenized and it is sterilized.
To carry out the present process, the said kernels may be chosen from the kernels of stone fruits such as peaches and apricots for example.
The said kernels may be ground, preferably after removing the skin and crushing in the dry state, in water at room or moderately high temperature, especially at 10-350xc2x0 C., in a suitable weight ratio, especially a ratio of {fraction (1/12)} to ⅓ for example, to obtain ground kernel matter in the water. To do this, a mill, a grinder or a high-speed stirrer such as a POLYTRON(copyright) type apparatus may be used for example. Preferably, two successive grindings are carried out so as to obtain a particularly fine aqueous dispersion of the ground matter.
The said aqueous extraction may be carried out at a pH greater or less than the isoelectric pH of the proteins of the said kernels, at room or moderately high temperature, for a time sufficient to allow the dissolution of most of the soluble matter of the said kernels, especially for one or more hours.
The insoluble matter may be separated by centrifugation, decantation, draining or filtration for example.
The said protein and/or lipid rich fraction may be isolated by isoelectric precipitation, namely at a pH equal to or close to the isoelectric pH of the proteins of the said kernels, or by tangential filtration, ultrafiltration and/or microfiltration. In the first case, the sugar rich supernatant may be separated by centrifugation, tangential filtration, ultrafiltration and/or microfiltration, and in the second case, the filtrate or the permeate may be directly separated for example.
In a first preferred embodiment of the present process, sweet apricot kernels are used. In this case, the said extraction is carried out preferably at pH 5-11 at 10-50xc2x0 C. for 1-5 h, the insoluble matter is separated from the aqueous extract, the protein and/or lipid rich fraction is isolated by precipitation at pH 3-5 at 10-50xc2x0 C. and the supernatant is separated.
In a second preferred embodiment of the present process, bitter apricot kernels are used. In this case, the said extraction is carried out preferably at pH 5-11 at 10-45xc2x0 C. for 1 to 10 h, hydrocyanic acid is separated from the aqueous extract by steam distillation or by distillation, the insoluble matter is separated by centrifugation, the protein and/or lipid rich fraction is isolated by tangential filtration, filtration and/or microfiltration, and the filtrate is separated.
The said aqueous extract or the said protein and lipid rich fraction may be skimmed for example. The skimming may be carried out at 4-60xc2x0 C., preferably at 35-45xc2x0 C. for example. This skimming may be performed with the aid of a centrifuge or a cream separator for example. Following such a skimming, the aqueous extract or the protein rich fraction and the cream may be stored at 1-5xc2x0 C. up to their use, for example.
In order to stabilize it by reducing the size of the lipid particles which it contains, the said protein and/or lipid rich fraction may be homogenized in a homogenizer, especially a piston homogenizer as manufactured by the company Rannie or the company Manton-Gaulin, in one or more passes at 50-1000 bar at 45-85xc2x0 C., preferably at 200-350 bar at 45-65xc2x0 C., for example.
In order to remove the bacterial load and to allow good storage in view of its use, especially in the food sector, the said protein and lipid rich fraction may be sterilized by heating at 80-160xc2x0 C. for 5 s to 60 min, preferably at 130-150xc2x0 C. for 20-80 s, for example.
Preferably, the said fraction is dried, after sterilization, to a residual water content of 1-7%. This drying may be carried out in a spray-drying tower, by freeze-drying or on a roller drier for example.
To facilitate the drying, in other words in order to be able to dry the said fraction without having to fear a separation of its lipid and protein phases, a drying aid may be added to it before homogenizing it, in an amount of 5-50%, preferably 10-30% by weight relative to the dry matter content of the fraction. A hydrocolloid such as xanthan gum or maltodextrin, for example, may be used as a drying aid.
It has been observed, surprisingly, that a protein and/or lipid rich fraction is thus obtained, in a dried form, having good self-emulsifying properties during its reconstitution.
The subject of the present invention is therefore also the use of all or part of a milk obtained by the present process for the production of a food product, especially for the production of products such as ice creams, dessert creams, coffee creams, mayonnaise sauces, salad dressings, flans, puddings or blancmanges for example.
The subject of the present invention is finally also a process for reconstituting a fraction enriched in lipid and/or protein of the said fruit kernels having a lipid/protein weight ratio of 0.05-3.5, by mixing a protein and/or lipid rich fraction isolated from the said aqueous extract with a cream obtained by skimming the said aqueous extract or the said protein and lipid rich fraction.